This invention relates in general to a gas metering device and to a device for supplying gas through a flow line to an outlet after it is measured in a measuring space and compared with gas accumulated in a pressure space.
A similar gas metering device is known from German patent application No. 32 29 328.3-35. The gas metering device can be employed anywhere, provided electrical control signals are available. Conventional change-over valves are used for switching.
The German application No. 32 29 328.3-35 discloses a gas metering device for medical apparatus, comprising a metering unit which is interconnected with the control unit, supplied through a pressure reducer with the gas to be metered, and delivers this gas in metered amounts through an outlet to a point of use. Within the metering unit, a buffer is connected to the pressure reducer at the supply side. At the other side, the buffer is connected through a throttle to a pressure space, and, through a change-over valve to a measuring space. The change-over valve is actuable by the control unit and upon switching, connects the meauring space through an outlet throttle to the outlet of the metering unit. A differential pressure sensor is connected through gas pipes to the pressure space and the measuring space, and delivers its electrical signals to the control unit.
During a metering cycle, the gas flows from the pressure source through the buffer and the change-over valve into the measuring space to fill it up. At the same time, a comparison pressure is maintained in the pressure space and safeguarded against instantaneous variations by a throttle. When the differential pressure sensor detects equal pressure in the pressure space and the measuring space, the control unit causes switching of the change-over valve. The gas then flows from the measuring space to the outlet, and the pressure in the measuring space drops. As soon as the pressure difference relative to the pressure space, and thus the signal from the differential pressure sensor, reaches a predetermined limit value, the control unit returns the change-over valve into its initial position, to start a new cycle.
The metered gas flow results from the volume of the metering space, the differential pressure in each cycle, and the switching frequency of the cycles. Unfortunately, the comparison pressure from the pressure space passes as filling pressure of the measuring space through the differential pressure sensor directly into the metered amount. The adjustment range is limited by the volume of the measuring space, for example. To enlarge the adjustment range, a plurality of independent metering units of different size may be provided in a metering device, and associated with a common control unit. The adjustment to a desired gas flow is then effected by selecting the suitable metering unit.